Magnetic alloy and devices utilizing same

ABSTRACT

Alloys having the nominal composition in weight percent 30 percent cobalt, 15 percent chromium, 5 percent manganese, 0.05 percent carbon, remainder iron, when cold worked to an area reduction of at least 50 percent and annealed at a temperature of 500 degrees to 650 degrees C. for a time of from one minute to 10 hours, exhibit a square hysteresis loop, medium coercive force, and high residual induction, enabling their use in a variety of magnetic devices such as bistable switches and memories.

United States Patent lnventors Appl. No.

Filed Patented Assignee Karl M. Olsen Madison;

Raymond C. Stofiers, Newark, NJ.

Nov. 26. 1969 June 28, 1971 Bell Telephone Laboratories, Incorporated Murray Hill, Berkeley Heights, NJ.

MAGNETIC ALLOY AND DEVICES UTILXZING SAME 7 Claims, 4 Drawing Figs.

US. Cl 335/154, 75/126, l48/3l.55

Int. Cl ..H01h 51/28 Field 05 Search 75/123 (K),

[56] W References Cited UNITED STATES PATENTS 3,170.1!2 2/1965 Bungardt et al. 75/126(H)UX 3,364,449 l/l968 Gould et al. 335/l53 Primary Exa'miner- Bernard A. Gilheany Assistant Examiner Roy N. Envall, .lr. Allorneys R. J. Guenther and Edwin B. Cave ABSTRACT: Alloys having the nominal composition in weight percent 30 percent cobalt, l5 percent chromium, 5 percent manganese, 0.05 percent carbon, remainder iron, when cold worked to an area reduction of at least 50 percent and annealed at a temperature of 500 to 650 C. for a time of from one minute to 10 hours, exhibit a square hysteresis loop, medium-coercive force, and high residual induction, enabling their use in a' variety of magnetic devices such as bistable switches and memories. 1

Patented June 28, 1971 2 Sheets-Sheet 1 F/GJ KM. OLSEN R. C. STOFFERS Patented June 28, 1971 2 Sheets-Sheet 2 FIG. 2

0.9 8 Lu 2 Lu 0: I I) 9, 0.8 I

l J 1 l l .02 .04 .06 .08 O.IO

PERCENT CARBON BY WEIGHT (NOMINAL) zoooo- F/G. 3

Ieooo- S D I- I Ieooog g g 5 -4o a Q E I40oo- & ao 2 3 a: g I2ooo U -20 IOOOO- L I l PERCENT CARBON BY WEIGHT (NOMINAL) MAGNETIC ALLOY AND DEVICES UTILIZING SAME Field of the Invention This invention relates to magnetic alloy materials having square hysteresis loops, medium coercivity and high residula induction, and to techniques for preparing them, and to devices using them.

Prior Art Recentinterest in devices which depend for their operation on remnant magnetic dlements, such as magnetic switching devices and memory elements, has spurred the development of various magnetic alloy materials to meet the needs of these devices. One such device is the ferreed switch described in Bell System Technical! Journal "Jan. 1960, pages 1 to 30. The bistable switching elements in these devices are required to have high residula induction, a medium coercive force, and a square hysteresis loop. The residual induction gives the magnetic elements the ability to remain magnetized after removal of an applied field, thus resulting in the maintenacne to switch closure The ease with which the material can be switched, that is the strength of the field required to reverse the nagnetization, is dependent upon the coercive force to the material. Typical requirements for such devices call for a coercive force within the range of to 50 oersteds, values intermediate between those commonly associated wit hard and soft magnetic materials. A-third requirement of these materials is that they possess a square hysteresis loop to insure against accidental switching by stray currents.

In U.S. Pat. No. 3,364,449 issued to H. S. B. Gould et al. on Jan. 16, 1968 is described an alloy which, when given certain critical processing steps, exhibits the magnetic characteristics required for use in the ferreed switch. The alloy has the. nominal composition 48 percent cobalt, 48 percent iron, 4 percent vanadium. The relatively high cobalt content makes this alloy expensive to produce.

In Techn. Mitt Krupp "18, 91-6, (1960 there was described a magnetic alloy containing only 30 percent cobalt, percent chromium and the balance iron. Unfortunately, ti has been found that alloy samples of this composition lack the requisite square hysteresis loop and that therein values of residual inductionand coercive force areinadequate for use as bistable switch elements in some applications.

The search continues to a suitablesubstitute for the expensive high cobalt-contaning Remendur alloy for use in the ferreed switch and other magnetic devices such as memory devices.

Summary of the Invention It has been discovered thath the control within critical limits of the carbon cintent of an alloy having the nominal compositionin weight percent percencobalt, l5 chromium, balance iron, markedly improves the squareness ratio of the hysteresis loop and increases the residual induction and coercive force of the alloy enabling its use in 1 magnetic devices such as switching devices andmemorises.

Brief Description of the Drawing FIG. 1 is a graph of induction in gauss versus coercive force inoersteds for various alloys of the invention containing varys e u ts tserbam.

FIG. 2 is a graph of squareness ratio rs) versus carbon content ofthe alloys ofthe invention. 7

FIG. 3 is a graph of residual induction in gauss and coercive force in oersteds versus carbon content of the alloys of the invention; and

FIG. 4 is a schematic diagram of one embodiment of a device known as a ferreed switch incorporating elements of the alloy of the invention.

DETAILED DESCRIPTION OF THE INVENTION The alloyrs of the invention may container from 20 to 35 weight percent cobalt below which the residual induction of the resultant alloy decreases to the extent that its use in the devices of the invention is of minimal utility, and above which the economic advantage of low cobalt content is no longer significant. Cobalt is preferred to be present within the range of 28 to 32 weight percent, for which optimum values for both residual induction and cold workability are attained. The alloy additionally contains from 10 to 25 weight percent chromium.

Lower concentrations will of necessity increase the iron content and thereby degrade the magnetic properties. Higher 'chromium contents will markedly impair the cold workability to the alloy. Chromium is preferred to be present within the range of 13 to 17 weight percent. The balance of the alloy contains substantially iron and carbon. The latter element is required in critical amounts to achieve the desired magnetic characteristics; While it will ordinarily be preferred to choose starting materials having little or no carbon present, and to add carbon in the proper amount of the melt, it will be appreciated by those skilled in the metallurgical arts that starting materials containing an excess of carbon may be chosed, and subsequently the carbon content adjusted to within the critical range by means of appropriate processing conditions. Carbon is present is in amounts from 0.007 to 0.2 weight percent, below which there is no significant effect upon magnetic properties and abo e which cold workability is appreciably impaired. Carbon is preferred to be present in amounts from 0.02 to 0.10 weight percent in order to achieve optimum magnetic properties. Below 0.02 weight percent the sqauremenss ratio of the hysteresis loop drops off rapidly as does the residual induction. Above 0.10 percent the coercive force may decrease and cold workability is impaired.

Various additional ingredients may be present in the alloy composition either as intentional additives or unintended impurities. Molybdenum, vanadium, niobium, titanius,, tantalum, and tungsten may be added in amounts up to about 7% 1 weight percent as partial substitutes for chromium for the e reasons normally associated with such additives by those skilled in the art. Vanadium may be preferred for its ability to reduce the hardness of the alloy, the us facilitating certain forming operations, such as punching Manganese may be present in amounts of up to l'percent in order to minimize the deleterious effect of any sulfur present in the alloy. However, 0.5 percent is adequate with no further advantage gained for larger amounts. As is known, any of several elements such as cerium, magnesium, beryllium and calcium may be substituted for manganese. Alternatively, manganese or its equivalent may be excluded entirely if sulfur content is sufficiently low. Sulfur should always be kept below 0.01 weight percent, however, and silicon should be kept below 0.2 weight percent, in accordance wit good commercial practice. Impurities should generally be kept below one weight percent total.

In addition to containing critical amounts of carbon, it is essential that the alloys be processed in accordance with the following teachings in order to attain the desired magnetic characteristics. The alloys must be cold worked by any of several methods such as rolling, drawing, swaging, etc. to an area recuction of at least 50 percent in accordance with the equation A0 A1 Z X 100,

where Z equals cold reduction in percent, A equals original cross section area, and A equals final cross section area. It is preferred to carry out cold working to an area reduction of at least percent in order to achieve optimum magnetic properties. This cold reduction must be followed by a partial terminal heat treatment, which may be of at a temperature of from 500C. to 650C. for a time of from 2 to 5 minutes at the upper temperature limit to about 5 to 10 hours at the lower temperature limit. Exceeding this range by too high a temperature or too long a time will result in a rapid decrease in residual induction and an increase .in coercive force. Conversely, inadequate heat treatment will result in an insufficient coercive force. It is preferred for the attainment of optimum properties to heat treat within the range of 520to 600C, for about I to 4 hours.

Minumum heat treating time is to some extent dependent upon the cross section of the body. While this is not critical for bodies adapted to use in the devices described herein, which do not generally exceed 0.05 inches in thickness, with substantially larger sections, heating time should be sufficient to permit the inner portion of the body to approach temperature equilibrium.

the above conditions apply to bulk heat treating. However, it is to be understood that conditions which result in equivalent heating are also acceptable. For example, as in strand annelaing, a thin continuous strand of the alloy may be passed very rapidly through a furnace at elevated temperature to accomplish the required heat treatment, as is known.

The essential steps of cold working followed by the partial terminal heattreatment may be preceded by any number of processing steps, including one or more thickness reductions followed by one or more softening anneals. However, it is stressed that the advantages of the invention may only be realized by concluding with cold working to an area reduction of at least 50 percent followed by the critical fianl heat treating step.

EXAMPLE A series of melts were prepared from electrolytic grades of cobalt, chromium, iron, and manganese in such proportions as to yield approximately 30 weight percent cobalt, l5 chromium, l/2 manganese, and balance iron. Carbon additions were made to the resultant molten alloys corresponding to about final 0.03 0.06 and weight percent of the melts. The alloys were then poured into steel molds to produce l /2 inches thick x 5 inches wide plates. The plates were, upon solidification, hot rolled at I200C. so as to reduce the thickness to 1/2 inch. The odice surface which had formed was removed by machining. Rods were then produced from the plates by cutting elongated bars from the plates, hot swaging at I200C. to 0.3 inch in diameter, grit blasting to remove the oxide films, annelaling for IS minutes at 950Cm ad and cold swaging to 0.09 inch in diameter. this cold working effected a 90 percent area reduction. The rods were then heat treated for two hours at 550C. and their magnetic properties measured. The results are shown in FIGS. lthrough 3.

Referring not wo FIG. I there are shown hysteresis loops for the rods containing carbon contents of about 0.007, 0.03, 0.06, and 0.1 weight percent. As may be seen with increasing carbon content the sqaUARENESS OF THE HYSTERESIS LOOP IS MARKEDLY IMPROVED. This squareness is conventionally expressed as a ratio of residual induction to saturation induction (B, lBs wherein B, is repreented on the FIG. as the point at which the loop intersects the positive B axis and B, being the point of highest value of B on the loop. This ratio is plotted against carbon content of the alloys of the invention in FIG. 2 It is seen that the squareness ration increases rapidly as the carbon content increases from 0.007 to abut 0.03 and thereafter increases gradually for higher carbon contents. A squareness ratio of at least 0.9 is preferred for optimum device operation and is readily achieved for a carbon content of approximately 0.03 Such a ratio is advantageous in that it substantially retam accidental switching between stable remanent states due to stray currents.

Referring now to FIG. 3 both residual induction and coercive force are plotted against carbon content of the alloys. It is seen that the induction increase very rapidly as carbon content increases from 0.0007 to about 0.03 percent and increases gradually thereafter for increasing carbon content. Coercive force increases rapidly up to a carbon content of 0.03 and decreases thereafter for increasing carbon content.

A residual induction of about l6,000 gauss and a coercive force of about 45 oersteds are preferred values for optimum device operation and correspond to carbon contents of about 0.03 to 0.l weight percent.

Referring now to FIG. 4 there is depicted schematically one embodiment which is illustrative of a ferreed switch. The

switch has a glass envelope 10 with terminals ll. A reed I2 ofv the alloy of the invention is attached to the left-hand terminal II. A second reed 13, which may be constructed of a soft magnetic material or of an alloy of the invention, is attached to the right-hand terminal ll so that its free end overlaps the free end of reed I2 to form a contact portion at 16. Also attached to the right-hand terminal '11 is a permanent magnet 14 having a magnetic polarity as shown. A coil 15 is would about the envelope 10 on the portion including the reed 12.

A complete description of the operation of this device is unnecessary to the invention and may be obtained by reference to US. Pat. No. 3,075,059 issued to S A. L. Blaha et al. on Jan. 22, I963, or the Bell System TECHNICAL JOURNAL" reference. Briefly, switch closure is accomplished by biasing coil 15 in such a manner that the magnetization direction of reed 12 corresponds with that of reed l3 (induced by permanent magnet 14). The residual induction of reed 12 results in a remanent magnetic field which to maintain closure must be sufficient to overcome the stiffness of the reeds. Reversing the direction of magnetization in reed l2 the other including reed 13, in which condition that natural stiffness of the reeds results in release.

The invention has been described in terms of a limited number of embodiments. As is known by those skilled in the art, the device depicted is but one of a large number of switching devices in which closur is maintained by means of the residual magnetic inudction of one or more associated elements. Devices known as induction switches comprise but one class of such devices and are themselves of many types. It is apparent from the description that the alloys of the invention may be used in all such devices in which a residual induction is sufficient to maintain electrical contact without application of a holding current, as well as in other devices which take advantage of the bistable characteristics of the material such as memory devices in which the direction of magnetization represents a binary l or 0.

We claim;

I. A magnetically remanent composition of matter consisting of in weight percent from l0 to 25 percent chromium, 20 to 35 percent cobalt, remainder iron, said composition having been produced by a series of processing steps terminating in a cold reduction of at least 50 percent followed by a heat treatment in a cold reduction of at least 50 percent followed by a heat treatment ast a t a temperature of from 500 to 650C. for a time of from 2 to 5 minutes at the highest temperature to 5 to ID hours at the lowest temperature, characterized in that said composition additionally contains controlled amounts of carbon of for 0.007 to 0.2 weight percent.

2. The composition of claim 1 in which the controlled carbon content is achieved ed by the addition of carbon as a separate constituent.

3. The composition of claim I wherein chromium is present in the amount of from 13 to 17 weight percent, cobalt is present in the amount of from 28 to 32 weight percent, and carbon is present in the amount of from 0.02 to 0.1 weight percent.

4. The composition of claim I in which the chromium is partially replaced by vanadium in the amount of up to 7 A weight percent.

5. The composition ofclaim l which contains up to 1.0 percent manganese, up to 0.2 percent silicon, and upo to 0.0l percent sulfur.

6. The composition of claim I in which the cold reduction is carried out to at least percent and heat treating is carried out to at a temperature of from 520 to 600C. for a time of from I to 4 hours.

7. A magnetic switching device comprising a magnetic circuit defining at least one magnetically remanent flux path including an element consisting essentially of the composition of UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,588,76'4 Dated June 28 19f].

In fl Karl M. Olsen, Raymond C Stoffers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column Line 1 11 change "Recentinterest to Recent interest-- 12 change "dlements" to --elements 16 change "'Iechnicall" to -Technical-- 22 change "maintenacne" to maintenance- 22 change "to switch" to --of switch-- 23 after "closure" insert a period 2Q change "nagnetiza" to -magnetiza- 25 change to the material" to "of thematerial 28 change "wit" to --with 2 change "H. s. B. to -H. L. B.-

36 change "The" to --This-- 42 "change "ti" to -it M change "therin" to -their- 45 change "inductionand" to --induction and-- FORM PC4050 USCOMM-DC 60376-7 69 Q U 5 GOVERNHENY PRINTING OFFICE I959 O-355'334 Page 2 UNITED STATES PATIENT OFFICE CERTIFICATE OF CORRECTION Inventofls) Karl M. Olsen, Ravmond C Stoffers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column Line 1 H6 change "areinadequate" to --are inadequate- 48 change "to a" to for' a-- 18 change "suitablesubstitute" to -suitable substitute-- 5 4 I change thath" to -that- 55 change "cintent" to -content 57 change tionin" to tion in-- 57 change "percencobalt" to percent cobalt-- 57 after "15" insert "percent-- 61 change "andmemories to -and memories-- II II 68 change (B to (B /B 2 3 change "alloyr's" to ---alloys-- 3 I chan e "container" to --contain-- 15 change "to the alloy, to -of the alloy.

19 after "characteristics" delete the semicolon and insert a period Patent No.

Inventor(s) change change after change change change at the at the change after after change change afteramounts delete Page 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated June 28 1971 Karl M. Olsen, Raymond C. Stoffers.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"of the melt" to -to the melt-- chosed to --chosen present" delete "is" abo e" to --above "squaremenss" to -squarenesstitanids, to titanium,

beginning of the line delete l" end of the line delete "e" the us" to -thus punching" insert a period llofll "recuction" to reductionwhich may be delete "of" FORM PO-OSO (10-69) Page UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pat nt N 3,588 16M Dated June 28, 1971 Inventor(s) Karl M. Olsen, Raymond C Stoffers It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column Line 3 1H before "above" change "the" to The-- 17 change "annelaing to -annealing-- 27 change "fianl" to -final-- 36 at the beginning of the line delete final 36 before "0.03" insert --o.o07,--

36 change "O11" to -O.l

&0 change "odice" to -oxide- M5 change "annelaling" to -annealing- M5 change "Cm ad" to -C,--

#6 after the period, change "this" to --This 50 change "not wo" to --now to- 53 change "sqaUARENESS OF THE HYS'TJERESISYI CO -squareness of the hysteresis-- 5 change "LOOP IS MARKEDLY IMPROVED" to -loop is markedly improved-- FORM PO-105O 10-69 Patent No.

Inventor(s) Column Page change change change after Karl M. Olsen,

CERTIFICATE OF CORRECTION Dated June 28 1971 Raymond C. Stoffers.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"(B /BS" to (B /B 'repreentec'i to represented "ration" to --ratio- "retarss" to --retards- "increase" to increases "0.0007 to --o.0o7-- "would" to -wound "s A. L." to --A. L.-

or" insert tochange "Bell System TECHNICAL JOURNAL" to Bell System Technical Journal" after reed 12" remove the comma and insert --results in two separate flux paths, the

one including reed 12,--

FORM PO-1050 (10-69) USCOMM-DC 50375-P69 u 5 GOVERNMENT FRINYING m'rmr was 0-555-334 UNITED STA??? PiTENT OFFICE CERTIFICATE OF CORRECTION Patent 3, 5 ,7 Dated June 28, 1971 lnventofls) Karl M, Olsen, Ravmond C. Stoffers.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1'.1 i r 1 e L 28 after "condition" change "that" to -the- 33 change "closur'" to --closur-e- 3U change "inudction" to -induction- 35 change "induction" to -;f'erreed- 45 change "We claim; to -What is claimed is:-

51 after "ment" delete the balance of the line 52 delete "heat treatment ast a t a" and insert at a 57 change "for 0.007" to -f:com 0.007

59 after "achieved" delete "ed" 70 change "upo" to -up- 7H after- "out" delete "to" Signed and sealed this 9th day of November 1 971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. Attesting Officer FORM PO-IOSO (10-69) ROBERT GOTTSCKALK Acting Commissioner of Patents USCOMM-DC 60376-969 n U 5 GOVERNMENT PRYNHNG OFFIFE U369 jBfiSbQ 

